Ah right, I thought you were going the other way - posting a link on Facebook from AB, but now I understand you want to put something on here, which is from FB.
If it's a link to a video, you can just copy the link and paste it on here, assuming it's not a direct link to FB, as some links on FB are directed to external sites, so copying onto here would meany anyone can see it.
However, if the link just takes you to FB, you'll probably have to download the video and then upload it to somewhere like youtube and then post that link on here.
I hope this makes sense :)